To find the relative atomic mass of an element, you need to consider the weighted average of the masses of its isotopes, taking into account their abundances.
Let's assume that the isotope with mass number 18 has an abundance of x, and the isotope with mass number 20 has an abundance of 2x. The sum of the abundances will be x + 2x = 3x.
The atomic mass of the isotope with mass number 18 is 18 amu, and the atomic mass of the isotope with mass number 20 is 20 amu.
To calculate the relative atomic mass (RAM) of element Z, you can use the following formula:
RAM = (mass of isotope 1 * abundance of isotope 1 + mass of isotope 2 * abundance of isotope 2) / (sum of abundances)
RAM = (18 * x + 20 * 2x) / (3x)
Simplifying the equation:
RAM = (18x + 40x) / (3x) RAM = (58x) / (3x) RAM = 58 / 3
Therefore, the relative atomic mass of element Z is approximately 19.33 atomic mass units (amu).